Microsoft KB Archive/105302
INFO: Canceling WaitCommEvent() with SetCommMask()
The information in this article applies to:
- Microsoft Win32 Application Programming Interface (API), used with:
- the operating system: Microsoft Windows NT, versions 3.1, 3.5, 4.0
- the operating system: Microsoft Windows 2000
If a serial port is in nonoverlapped mode (without FILE_FLAG_OVERLAPPED) and SetCommMask() is called, the call does not return until any pending WaitCommEvent() calls return. This apparently contradicts the following statement from the SetCommMask() Help
If SetCommMask() is called for a communications resource while a wait is pending for that resource, WaitCommEvent() returns an error.
and the following statement from the WaitCommEvent() Help:
If a process attempts to change the device handle's event mask by using the SetCommMask() function while a WaitCommEvent() operation is in progress, WaitCommEvent() returns immediately.
However, this is the expected behavior. If you open a serial port in the nonoverlapped mode, then you can do only one thing at a time with the serial port. SetCommMask() must block while the WaitCommEvent() call is blocking.
If the serial port was opened with FILE_FLAG_OVERLAPPED, WaitCommEvent() will return after SetCommEvent() has been called.
The SDK 3.51 docs have been corrected.
Additional query words: 3.10 3.50 com1 com2
Keywords : kbAPI kbCommPort kbKernBase kbOSWin2000 kbDSupport kbGrpDSKernBase kbSerial
Issue type : kbinfo
Technology : kbAudDeveloper kbWin32sSearch kbWin32API
Last Reviewed: October 27, 2000